Electro-optical transmission system and apparatus



April 21, 1942. 2,280,688

ELECTRO-OPTIGAL TRANSMISSION SYSTEM AND APPARATUS A. G. COOLEY. E AL 2Sheets-Sheet 1 Filed Jan. 6, l940 N A A ra/3'57 April 21,1942. A. G.COOLEY ET AL 2,230,688

ELECTRO-OPTIGAL TRANSMISSION SYSTEM AND APPARATUS Filed Jan. 6, 1940 2Sheets-Sheet 2 TOPQUE SPEED A TTORNEY Patented Apr. 21, 1942ELECTED-OPTICAL TRANSMISSION SYSTEM AND APPARATUS Austin G. Cooley, NewYork, and Gsrett Vander Veer Dillenback, Jr., Slingerlands, N. Y.,assignors, by mesne assignments, to Times Telephoto Equipment Inc., NewYork, N. Y., a corporation of New York Application January 6, 1940,Serial No. 312,648 (Cl. rza-aasi 2 Claims.

This invention relates to electro-optical systems, and more especiallyto systems for transmitting visual representations to a distance andreproducing facsimiles thereof by electro-optical means.

A principal object is to provide an improved motor drive for thescanning mechanism of a facsimile system or for the rotary signallingdevice of any other similar signalling system.

Another object is to provide an improvedinduction-motor-synchronous-motor combination to facilitate attainingand maintaining synchronous speed of associated signalling equipment.

Another object is to provide an induction-motor drive and method ofadjusting the torquespeed characteristic so as to correlate it with thesynchronous frequency of an associated synchronous motor.

A feature of the invention relates to the novel organization,arrangement and relative interconnection and adjustment of parts wherebya facsimile scanner or similar rotatable signalling device can bebrought to, and maintained at, synchronous speed.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims.

' In the drawings which show one preferred embodiment of the invention,

Fig. 1 is a schematic composite circuit and apparatus diagram toillustrate certain features of the invention.

Fig. 2 is a schematic diagram of the motor drive of Fig. 1 to explainthe method of adjusting the characteristics of the induction-motorportion of the drive.

Fig. 3 is a curve explanatory of the operation of Fig. 2.

Referring to Fig. 1, there is shown in schematic form, a facsimiletransmission system embodying the various features of the invention. Thetransmitting drum l around which the picture or-other subject-matter iswrapped, is rotated about its axis, from the motor ll through the wormwheel 2 and the replaceable worm drive 3. A stroboscopic indicator wheel4 is also carried as a unit by the replaceable worm and is illuminatedby the stroboscopic lamp Swhich may be energized by currents from asource whose frequency is known. The members 3 and 4 form a readilyreplaceable unit with the stroboscope wheel definitely related to thepitch of the worm 3. The line feed for the illuminating optical scanningsystem 6 is effected by gear wheel I and gear wheel I, the latter beingfastened to the lead screw I to feed the system 0 which may be of anywell-known construction.

Associated with the drum l is any well-known form of light sensitivepick-up and modulating arrangement I. Preferably, although notnecessarily, motor ll drives an A. C. generator (not shown), forexamplea generator of 1800 cycle current which is fed to the apparatusl0 over the conductors l2 whereby the 1800 cycle current is modulated inthe device 10 in accordance with the intensity of the light reflectedfrom each successive elemental area of the picture on drum l. A detaileddescription of such modulating system is given in PatentNo. 2,015,742.

The amplified picture currents which are impressed on the transmissionchannel ll, therefore, have a carrier frequency which is locked to thespeed of drum l, since the motor which drives drum I also drives the A.C. generator. Consequently, as described in said Patent No. 2,015,742,these currents may be used to control the recording lamp at the receiveras well as to synchronize the receiving apparatus with the transmitter.

- The receiver includes a rotatable drum ll which is mounted forrotation about its axigin suitable bearings and is driven by a wormwheel I5 carried by the drum shaft, which worm wheel is driven by a worml6. Drum I4 is brought up to speed by a two-speed induction motor llhaving two sets of windings for the respective speeds. A common terminalI8 is provided for both windings and individual terminals l9 and 20 areprovided for the other windings, these latter terminals beingselectively connectable to the supply line by a switch 2|. Preferably, avariable resistance Hg is connected in circuit with the 7 commonterminal and the primary of motor l1, and a variable resistance 28 isconnected in circuit with the secondary winding of motor H, for purposesto be described.

When the switch 2| is in the full line position the motor II willrotate, for example at 1800 R. P. M. which would be equivalent to 45 R.P, M. for the drum ll. When the switch 2| is in the dotted position, themotor l1 rotates at 3600 i'riction from the various bearings, windage,etc. The remaining steady load and all load variations such as caused byslight speed changes at the transmitter, as well as power supplyvariations. are taken by the synchronous motor 22.

The stator winding 23 of the synchronous motor is supplied with part ofthe received picture carrier current through a double-pole switch 24when the latter is in the full-line position shown. It will beunderstood of course. that the received signals are suitably amplifiedin amplifiers 25, 26, and preferably the ampliiier 26 which feeds thestator 23 is biased as will be described in detail hereinbelow inconnection with Figs. 2 and 3. This bias is related to the resistance 28in circuit with the wound rotor of induction motor I! as will also bedescribed below so as to operate the motor I! on a predetermined portionof its torque-speed characteristic curve. The motor I I will then beconstrained to run at or near the synchronous speed of the motor 22, thelatter acting as a speed control for the induction motor. Consequently,as the drum it approaches the synchrono'us speeds, the motor 22 readilyfalls into step with the received signal.

The position of recording lamp 29 is controlled by the line feed screw30 driven through worm-wheel 3| and worm 32 from a two-speed inductionmotor 33 similar to motor l1. Motor 33 is provided with a. switch 34 soas to connect in circuit either the low or high speed winding asdesired. The lamp 29 is energized from its associated amplifier 21.

It will be assumed for purposes of illustration, that in the arrangementas shown, drums I and I4 are being driven at 90 R. P. M. and that thegenerator which supplies the carrier current to device l delivers an A.C. of 1800 cycles. Under this assumption therefore, switches 2|, 24 and24, are in their dotted line positions whereby motors l1 and 33 rotateat approximately 3600 R. P. M. Should it be desired to change the speedof rotation of the drum l to 45 R. P. M., the double-thread worm andstroboscope assembly 3, l, is removed by loosening thumb nut 35,- and isreplaced by a single-thread worm as described in detail in applicationSerial No. 261,184, filed March 11, 1939. When the switch is in thisfull line,position, an 1800 cycle signal will be supplied to thesynchronous motor 23,, 22. When it is in the dotted line position, thecoil 33 will pick up a 3600 cycle signal from the phonic wheel generator33, 39, which is driven by the synchronous motor 36, 31. At thereceiver, the speed can be reduced to 45 R. P. M. when the switch 24 isthrown to its full line position, so as to supply 1800 cycle signal tothe motor 23,, 22. Switches 2| and 34 will also have to be thrown to thefull line position. When in this position, motor I! will be brought upto a speed approximating synchronous speed of the motor 23, 22. motorwill take control of the speed of the drum. The speed of the line feedmotor will also be changed to produce a scanning line feed correspondingto that oi the transmitter.

As described above, in connection with Fig. 1,

the assembly comprising the induction motor IT and the synchronous motor22-23, is preferably adjusted so as to operate on a particular portionof the speed-torque characteristic curve of the induction motor. Atypical speed-torque characteristic of such a motor is shown in Fig. 3,and preferably, the motor is designed and is provided with adjustablemeans so as to enable it to run at the proper point. Since thesynchronous speed is to be determined by the speed l-of the receivedcarrier current, the synchronous motor rotor 22 is mechanicallyconnected to the shaft 22a of the A. C..induction motor-l1. It isdesirable that the synchronous motor 22 should come into synchronismwith the received carrier without any unnecessary attention on the partof an attendant, and also in the event that the synchronizing signalshould fail ,for a short time, that the motor I! automatically will fallinto synchronism when the synchronizing signal is reestablished. Forthis purpose, the incoming signal received over line I3 is fed into anamplifier 26 which has its control grid 26a biased preferably negativelywith respect to the cathode 26b, for example by the negative gridbattery 260, so that in the absence of a synchronizing signal applied tothe grid 260, a steady magnetizing current flows through winding 23. Theanode circuit of tube 26 includes the stator winding 23 of thesynchronous motor. The induction motor may comprise the wire woundsecondary "a and a primary winding 1b, the latter being connected to asource of power "d of fixed frequency or through an adjustable resistor51g to a source of power oi a controllable frequency. The slip ringslle, I'If, connect the secondary winding in with the variable resistance28 to permit adjustment of the torque-speed characteristic of the motor.The resistance 23 is adjusted so that when no signal is applied to thestator winding 23 of the synchronous motor, the induction motor I!drives the assembly at slightly above synchronous speed at which timethe motor operates at point P of its characteristic curve (Fig. 3). Theinduction motor will not tend to run much above this point in speed,because the torque will limit the speed to the indicated point. In caseswhere the resistance 28 can be fixed at a given point, it is desirableto include the resistance in the rotor itself to eliminate the necessityof the slip rings "a and II This can be done in any conventional manner;such as using brass bars in a squirrel cage rotor, or spacing the barsaway from the rim of the rotor, or increasing the air gap between therotor At this point, the synchronous and stator. When the synchronizingsignal is applied to the stator 23, there will be exerted anelectro-magnetic drag on the rotor 22 which causes the assembly to slowdown gradually. As the speed of the assembly approaches synchronousspeed, that is, the synchronous speed of rotor 22, the motor I! readilyfalls into step with the applied signal, which point is indicated by theletter "S (Fig. 3). Preferably, the rotor 22 is coupled to the shaft 22aby any wellknown form of spring coupling diagrammatically indicated bythe numeral 22b.

While in the foregoing description the method of operation has beenpredicated upon the continuous operation of the induction motor I! whichis maintained at synchronous speed by the synchronous rotor 22 this isnot necessary in all cases. For example, if the synchronous motor 22,23, is of the type disclosed in application Serial No. 299,955, filedOctober 18, 1939, it may be made of such high efliciency that by itselfit will provide suflicient power to maintain the drum is in synchronismin which event the switch 2| will be moved to open circuit position whenthe drum H has been brought to synchronous speed and the receivedsynchronizing imthat the induction motor I! is adjusted so thatits slipspeed is slightly above the synchronous speed of the synchronous motor,it will be understood that the invention may also be employed byadjusting the resistance 28 or designing the induction motor l1 so thatits slip speed is slightly below the said synchronous speed. Under thesecircumstances, the induction motor merely serves to bring the drum Inearly up to synchronous speed whereupon the synchronous motor 22 whichis driven by the received synchronizing impulses, brings the mechanicalsystem including drum I! to synchronous speed. In this arrangement, thespring coupling 22b has been found important since without it, it wouldbe very difllcult for the synchronous motor topull the mechanical systemincluding the rotor of induction motor ll up to the proper synchronousspeed. Preferably, although not necessarily, the spring coupling 22bbetween the synchronous motor shaft and the induction,

motor shaft is provided with any well-known form of dampening means inorder further to insure the proper operation of the mechanism.

While certain specific embodiments have been described herein, it willbe understood that various changes and modifications may be made withoutdeparting from the spirit and scope of the invention. This applicationis a continuation-in-part of application Serial No. 261,184, filed March11, 1939.

What we claim is:

1. In combination, a, synchronous motor having a toothed rotor and astator winding adapted to be normally excited by D. C. polarizingcurrents, means to receive synchronizing impulses, a. grid-controlledamplifier tube upon which said impulses are impressed, the said statorwinding being connected in the plate circuit of said tube to be excitedby the normal steady space current thereof even in the absence ofsynchronizing signals, an induction motor, the rotor of said synchronousmotor being resiliently coupled to the rotor of said induction motor,and means to adjust thecharacteristics of the induction motor so that itnormally runs at a speed slightly higher than the maximum torque-speedin the absence of said synchronizing signals.

2. The combination according to claim 1 in which the control grid ofsaid tube is biassed to permit a polarizing current to flow through thestator of the synchronous motor.

AUSTIN G. COOLEY. GARET'I' VAN'DER VEER DILLENBACK. JR.

